Twitter and other social media companies have so far refused to engage with the government’s plans to introduce age checks to limit underage access to online pornography, an organisation that strongly influenced the rules has said.

Lord Erroll, a crossbench peer who chairs the Digital Policy Alliance (DPA) – a thinktank that has collaborated with the government to draft the rules on age verification (AV), admitted the ultimate sanction intended for sites that fail to implement AV is unlikely to be applied to Twitter.

Unlike Instagram and Facebook, Twitter has no rules against the posting of sexually explicit material and hosts many accounts that promote publishers and stars of pornography.

“The challenge with that is if you block Twitter, people will just say this is an overreaction, it’s mad, and it would not go down well in public,” Erroll said.

The other option would be to tell credit card companies to withdraw payment services. However, Erroll admitted that such a penalty was intended for recalcitrant pornography sites, rather than the likes of Twitter and Snapchat.

Rudd Apsey, a DPA director, said Twitter had been “a particular challenge”, although it would be included under the AV rules as an “ancillary service provider”.

“We as an industry would like to see more verification in that space,” he said. “But at this stage, they haven’t approached us about it.”

Twitter said it had tools to limit the visibility of low-quality content. Adult material is classed by the company as “sensitive”.

Apsey and Erroll spoke at a showcase of AV services, which will soon become mandatory for all pornographic websites. The requirement had been due to be enforced in April, but the Department for Digital, Culture, Media and Sport announced this week that it would be pushed back to an unspecified date later this year.

All the products demonstrated would abide by a new code of practice (PAS 1296), which has been sponsored by the DPA and is due to be published on Monday. Apsey stressed the privacy aspect of the technologies, which would separate identity providers and websites, to prevent either side from building a database of users’ pornography browsing history.

The industry faces a battle to gain the trust of consumers. Polling carried out in January by a broadband comparison site found 56% of web users would not trust their details with third-party AV services.

Absent from the showcase was AgeID, the AV solution developed by MindGeek, the world’s biggest pornography publisher. Observers expect AgeID will become the market leader once age checks become mandatory, since MindGeek controls several of the most popular porn sites.

The regulatory environment surrounding age checks on pornography is still unclear, with the British Board of Film Classification, appointed to regulate the policy, only now consulting on guidance for the industry.

There is no requirement for sites to offer multiple means of AV, or strict rules on anonymity beyond those stipulated by the General Data Protection Regulation, which comes into force in May.

Jim Killock of the Open Rights Group said the GDPR would provide only general rules unsuited to the particularly sensitive information involved in the age verification of pornographic websites.

Among those opposed to the AV requirements have been small-scale pornogtraphy producers. Erika Lust, a Swedish director of feminist-influenced pornography, said the rules as currently drafted would cement the dominance of MindGeek over the industry, whose output mostly consists of pornography “made by men for men”.

“This will only get worse as MindGeek continue to infiltrate the market, and smaller, independent sites are forced to close if they cannot afford age verification software,” she said.